1. Field of the Invention
The present invention relates to a refrigerant evaporator used in a refrigeration cycle, more particularly relates to a refrigerant evaporator adapted for an air-conditioning apparatus for an automobile.
2. Description of the Related Art
Conventionally, as the evaporator used in the refrigeration cycle of an air-conditioning apparatus etc., an evaporator wherein a plurality of cores, each forming a refrigerant passageway through which the refrigerant passes by superimposing two flat plate type core plates, and corrugated fins are alternately stacked has been known. In such an evaporator, the distribution of the refrigerant to the refrigerant passageways is apt to become nonuniform. To prevent this, for example, a means as disclosed in Japanese Examined Patent Publication (Kokoku) No. 58-41429 has been considered. In this evaporator, narrow, very small passageways constituting fixed throttles are formed in the core plates, the refrigerant condensed and liquidized by the condenser is sent as is to the evaporator and distributed so that the amount of the refrigerant to the respective refrigerant passageways becomes uniform by the fixed throttles of each core, and, at the same time, the pressure is reduced at those parts.
In a refrigeration system, on the other hand, to achieve an improvement of performance, it has been proposed to reduce as much as possible the gas refrigerant not relevant to the cooling, generated after the receiver, and to thus increase the amount of the effective refrigerant by providing a heat exchanging means for performing the heat exchange between a high temperature piping at an outlet of the receiver and a low temperature piping between the evaporator and a temperature sensing tube to perform so-called supercooling (Journal of Nippondenso Technical Disclosure 40-076, issued on Mar. 15, 1985).
However, in such a conventional evaporator provided with fixed throttles, if a refrigerant in a gas-liquid two-phase state flows into these fixed throttles, a uniform distribution of the refrigerant cannot be achieved. Namely, there is a problem in that fixed throttles through which a large amount of gaseous state refrigerant passes and fixed throttles through which a large amount of liquid state refrigerant passes are produced.
Therefore, it can also be considered to make the distribution of the refrigerant by the fixed throttles more uniform by using the aforesaid evaporator provided with the fixed throttles in the aforesaid refrigeration cycle, cooling the refrigerant after the receiver by a low temperature refrigerant passed through the evaporator by the heat exchanging means, and perform supercooling, thereby increasing the amount of the liquid state refrigerant.
However, when the temperature of the air cooling the condenser is uniformly low, i.e., 0.degree. to 10.degree. C. as in the winter season, the liquidization of the refrigerant is excessively promoted so that the amount of refrigerant supplied to the evaporator sometimes becomes insufficient. Also, in a transitory operation state, there sometimes occurs a case where the amount of refrigerant supplied to the evaporator is insufficient due to the shortage of liquid in the receiver.
In such a case, sometimes the temperature at the outlet of the evaporator rose and the refrigerant passed through the receiver could not be sufficiently cooled by the heat exchanging means. Alternatively, there was the problem that the temperature of the outlet of the evaporator sometimes became higher than the temperature of the refrigerant passed through the receiver, to conversely evaporate the refrigerant passed through the receiver, resulting the performance of the evaporator being greatly lowered.
Also, in the aforesaid conventional evaporator, fixed throttles were formed in two flat plate type core plates provided with concave portions. To effect uniform distribution, however, the plurality of fixed throttles have to be formed so as to have precisely the same cross-sectional surface area, so they conversely will become a cause of nonuniform distribution. The two core plates, for example, are bonded by brazing, and therefore there arose a problem in production such that the brazing material splattered on these fixed throttles, to make the formation of identical fixed throttles having the correct cross-sectional surface area difficult.